1. Field of the Invention
The present invention relates to a magnetic disk device such as a levitation type magnetic disk device using a levitation type magnetic head, a load/unload type magnetic disk device and a contact type magnetic disk device using a contact type magnetic head. In the following description, a magnetic head slider is simply called a "slider".
2. Description of the Related Art
A recent improvement of a memory density has been significant in a magnetic disk device. One factor for improving a line recording density of a magnetic recording is a reduction of a magnetic separation length (the magnetic separation length=a thickness of a magnetic disk protective film+a thickness of a magnetic disk lubricating film+an amount of magnetic disk levitation+a thickness of a slider protective film). In a conventional levitation type magnetic disk device, the magnetic disk device intends to improve the line recording density by reducing a levitation loss of a magnetic head to a limit. this is a contact type magnetic disk device using a contact type magnetic head.
Both of the protective film thickness and the amount of. levitation are reduced, thereby resulting in the reduction of reliability and longevity of the magnetic disk device with a mechanical contact slide. Thus devised is means for ensuring the reliability and longevity in even an environment wherein the protective film thickness and the amount of levitation are lower. One example is a load/unload type magnetic disk device as described in Japanese Patent Application Laid-open No. 1-185888/1989. Unlike the conventional magnetic disk device using a CSS (Contact Start Stop) system, the load/unload type magnetic disk device is provided with a mechanism for loading/unloading a levitation type magnetic head to a disk surface when the magnetic disk starts and stops rotating. This thereby intends to reduce a mechanical damage caused between the magnetic head and the magnetic disk during the CSS operation which the conventional magnetic disk device suffers from.
In the conventional magnetic disk device using the CSS system, attention is also paid to a reliability technique in which drive states of the device (the CSS operation and seek operation) are controlled in consideration of its operating condition whereby the technique attempts to improve the device longevity.
For example, in the technique disclosed in Japanese Patent Application Laid-open No. 6-52644/1994, Japanese Patent Application Laid-open No. 4-134677/1992, Japanese-Patent Application Laid-open No. 4-111272/1992 and Japanese Patent Application Laid-open No. 63-239618/1988, the CSS operation is controlled whereby the reliability is improved.
In the technique disclosed in Japanese Patent Application Laid-open No. 6-52644/1994 and Japanese Patent Application Laid-open No. 4-111272/1992, two regions for the CSS operation are disposed on the magnetic disk. The mechanical damage, which typically focuses on a single CSS region, is distributed into two CSS regions whereby this technique attempts to improve the longevity. In the technique disclosed in Japanese Patent Application Laid-open No. 4-134677/1992, the CSS operation is performed on an optional position all over the magnetic disk surface so as to distribute the damage all over the disk surface whereby the reliability is improved. In the technique disclosed in Japanese Patent Application Laid-open No. 63-239618/1988, when the magnetic disk is not rotated, the magnetic head is stopped in the region where a surface roughness of the magnetic disk is significant. The magnetic head is moved to the smooth region of the magnetic disk prior to the rotation, where the CSS operation is performed. This prevents the magnetic head and magnetic disk from contacting each other when the magnetic disk is not rotated. Furthermore, the magnetic head is started in the smooth region whereby a good CSS specific value can be obtained.
In the technique disclosed in Japanese Patent Application Laid-open No. 4-291069/1992, the number of rotation of the magnetic disk is changed except during a recording/reproduction, that is, when no access is given to the magnetic disk. The amount of slider levitation during no access is larger than the amount of slider levitation during the recording/reproduction, whereby the technique intends to reduce a probability of contact slide. More specifically, when a floating dust in the device is present in a levitation space, the damage resulted from the contact slide is reduced.
In the technique disclosed in Japanese Patent Application Laid-open No. 3-225669/1991, when the number of rotation of the magnetic disk is the number of steady rotation or less, that is, in a state before the slider reaches to a complete levitation with respect to the magnetic disk, the seek operation is performed. The dust adhering to the magnetic head and the magnetic disk is removed, whereby the technique intends to improve the reliability. Other means for improving the reliability by the seek operation is the seek operation during the no access which is already incorporated in the actual magnetic disk device. When a non-access state is continued in a predetermined time interval during a rotating operation of the magnetic disk device, the seek operation is automatically performed. A specified disk diameter reduces the probability that the disk is subject to the continuous contact slide for a long time. The seek operation also intends to remove the dust adhering to the magnetic head.
The technique for intending to improve the reliability of the load/unload type magnetic disk device is a system which considers a load/unload timing chart as described in Japanese Patent Application Laid-open No. 6-203503/1994. In this load/unload type magnetic disk device, a load operation is performed from the time when a tangential force acting on the magnetic head is maximum to the time immediately before it is minimum. An unload operation is performed from the time immediately after the tangential force restarts to increase to the time when the tangential force is again maximum, whereby the damage is prevented and a deposit on the head is removed.